THE BRYOPHYTES 271 
encounters what is known as alternation of generations.) 
By this is meant the descent of a spore-bearing plant, or 
sporophyte, from a sexual plant, or gametophyte, then the 
descent of a gametophyte from the sporophyte, and so on 
indefinitely (see Sect. 357).2- In Marchantia the sporophyte 
is a minute organism, incapable of separate existence and 
living much like a parasite : 
on nourishment drawn from 
the female receptacle. 
350. Summary of the Liv- 
erworts. — The liverworts 
show a distinct advance in 
complexity over the alge. 
This appears particularly in 
the excellent facilities pos- 
sessed by such forms as Mar- 
chantia for photosynthesis 
and respiration, as land 
plants. It is also shown by 
the complicated process of 
sexual reproduction, matur- 
ing the egg in a many-celled 
archegonium and not in a 
one-celled organ such as is 
found among the thallophytes 
(e.g. Fig. 163). Alternation of generations is another in- 
dication of an advanced position in the plant world. It 
is important to note that while the majority of liverworts 
are terrestrial they all have ciliated sperms, a characteristic 
Fie. 196. A Small Portion of 
Fig. 195 enlarged. 
8, the stalked spore-capsule. 
1This also occurs in a less evident form in red alge and in some sac 
fungi. 
. 2 The student may be asked to make a diagram of the life history of Mar- 
chantia on the plan of Fig. 203, or an illustrated one somewhat like Fig. 208, 
